Protection element

ABSTRACT

The present invention aims to achieve a Pb-free protection element by using a layered body including a high melting point metal layer and a low melting point metal layer. A protection element includes an insulating substrate, a heating body, an insulating member, two electrodes, a heating body extraction electrode, and a fusible conductor. Furthermore, the fusible conductor includes a layered body including at least a high melting point metal layer and a low melting point metal layer, and the low melting point metal layer is melted by a heat generated by the heating body, whereby, while eroding the high melting point metal layer, the low melting point metal layer is drawn close to the side of the two electrodes and the heating body extraction electrode, and fused, the two electrodes and the heating body extraction electrode each having high wettability for the low melting point metal layer.

This application is a continuation application of U.S. patentapplication Ser. No. 14/387,797 filed Sep. 24, 2014, which is in turn aU.S. National Stage of International Application No. PCT/JP2013/059013filed Mar. 27, 2013, which claims the benefit of Japanese PatentApplication No. 2013-008302 filed Jan. 21, 2013, Japanese PatentApplication No. 2012-281452 filed Dec. 25, 2012, and Japanese PatentApplication No. 2012-076928 filed Mar. 29, 2012. The disclosure of theprior applications is hereby incorporated by reference herein in theirentirety.

FIELD OF THE INVENTION

The present invention relates to a protection element which fuses acurrent path to stop charging a battery connected on the current path,thereby controlling thermal runaway of the battery.

BACKGROUND OF THE INVENTION

Most of secondary batteries, which are capable of being charged andthereby repeatedly used, are processed to be in the form of a batterypack and provided to users. In order to secure the safety of users andelectronic devices, particularly in a lithium ion secondary batteryhaving high weight energy density, some protection circuits forovercharge protection, overdischarge protection, and the like aregenerally built in a battery pack, and said battery has a functioncapable of interrupting the output of the battery pack in apredetermined case.

Using an FET switch built in the battery pack, the output thereof isturned on and off, whereby an overcharge protection operation or anoverdischarge protection operation of the battery pack is performed.However, in the case where the FET switch is short-circuited and brokendue to some reason; in the case where application of a lightning surgeor the like causes a high current to instantly flow; or in the casewhere an output voltage extraordinarily decreases due to the life of abattery cell, or, on the contrary, in the case where excessive voltageis outputted, the battery pack and the electronic device must beprotected from accidents, such as fire accidents. Therefore, in order tosafely interrupt the output of a battery cell in any thus-postulatedabnormal situation, a protection element comprising a fuse element has afunction to interrupt a current path using an external signal.

As disclosed in Patent Literature 1, for such protection element of aprotection circuit for lithium ion secondary batteries and the like,there has been generally employed a structure which has a heating bodyinside a protection element and a fusible conductor on a current pathusing this heating body.

PRIOR ART DOCUMENTS Patent Document

PTL 1: Japanese Patent Application Laid-Open No. 2010-003665

PTL 2: Japanese Patent Application Laid-Open No. 2004-185960

PTL 3: Japanese Patent Application Laid-Open No. 2012-003878

SUMMARY OF THE INVENTION

In the protection element disclosed in Patent Literature 1,Pb-containing solder having a high melting point of not less than 300degrees C. is generally used for a fusible conductor so that, whenreflow mounting is applied, the fusible conductor is not melted by theheat of the reflow. However, in RoHS Directive and the like, the use ofPb-containing solder is only limitedly permitted, and accordingly demandfor Pb-free soldering is expected to intensify.

Here it should be noted that “solder erosion” and “ erosion phenomenon”have been ever well known as a phenomenon in which Au plating or Agplating of electronic parts or the like begins to melt into moltensolder, and Patent Literature 2 discloses a protection element providedas a Pb-free soldering material obtained by taking advantage of thisphenomenon. However, as described in Patent Literature 2, there is aproblem associated with a structure in which a high melting point metallayer arranged so as to closely adhere to an insulating layer leads onlyto an erosion phenomenon of the high melting point metal layer caused bymelting of a low melting point metal layer, and sometimes fails incomplete interruption of a circuit. Furthermore, in order to surely fusea fusible conductor, it is preferable to form a slit, a film thicknesslevel difference, or the like in a high melting point metal layer or thelike, but, there is a problem associated with an increased step forformation of a slit or a film thickness level difference (for example,refer to Patent Literature 3).

Then, the present invention aims to achieve a Pb-free protection elementby using a layered body comprising a high melting point metal layer anda low melting point metal layer.

To solve the above-mentioned problems, a protection element according toan embodiment of the present invention comprises: an insulatingsubstrate; a heating body laminated on the insulating substrate; aninsulating member laminated on the insulating substrate so as to coverat least the heating body; first and second electrodes laminated on theinsulating substrate having the insulating member laminated thereon; aheating body extraction electrode laminated on the insulating member soas to be superimposed with the heating body, and electrically connectedto the heating body on a current path between the first and secondelectrodes; and a fusible conductor laminated over a range from theheating body extraction electrode to the first and second electrodes,and fusing the current path between the first and second electrodes byheating. Furthermore, the fusible conductor comprises a layered bodyincluding a high melting point metal layer and a low melting point metallayer, and the low melting point metal layer is melted by a heatgenerated by the heating body, whereby, while eroding the high meltingpoint metal layer, the low melting point metal layer is drawn close tothe side of the first and second electrodes and the heating bodyextraction electrode, and fused, said first and second electrodes andsaid heating body extraction electrode each having high wettability.

It is preferable that the low melting point metal layer is made of aPb-free solder, meanwhile the high melting point metal layer is made ofa metal containing Ag or Cu as a main component.

Furthermore, the volume of the low melting point metal layer ispreferably larger than the volume of the high melting point metal layer.

A protection element according to another embodiment of the presentinvention comprises: an insulating substrate; a heating body laminatedon the insulating substrate; an insulating member laminated on theinsulating substrate so as to cover at least the heating body; first andsecond electrodes laminated on the insulating substrate having theinsulating member laminated thereon; a heating body extraction electrodeelectrically connected to the heating body on a current path between thefirst and second electrodes; and a fusible conductor laminated over arange from the heating body extraction electrode to the first and secondelectrodes, and fusing the current path between the first and secondelectrodes by heating. Furthermore, the fusible conductor comprises alayered body including at least a high melting point metal layer and alow melting point metal layer. The low melting point metal layer ismelted a heat generated by the heating body, whereby, while eroding thehigh melting point metal layer, the low melting point metal layer isdrawn close to the side of the first and second electrodes and theheating body extraction electrode, and fused, said first and secondelectrodes and said heating body extraction electrode each having highwettability for the low melting point metal.

A protection element according to another embodiment of the presentinvention comprises: an insulating substrate; a heating body laminatedon the insulating substrate; an insulating member laminated on theinsulating substrate so as to cover at least the heating body; first andsecond electrodes laminated on the insulating substrate having theinsulating member laminated thereon; a heating body extraction electrodeelectrically connected to the heating body on a current path between thefirst and second electrodes; and a plurality of fusible conductorslaminated over a range from the heating body extraction electrode to thefirst and second electrodes, and fusing the current path between thefirst and second electrodes by heating. Furthermore, each of the fusibleconductors comprises a layered body including at least a high meltingpoint metal layer and a low melting point metal layer. The low meltingpoint metal layer is melted a heat generated by the heating body,whereby, while eroding the high melting point metal layer, the lowmelting point metal layer is drawn close to the side of the first andsecond electrodes and the heating body extraction electrode, and fused,said first and second electrodes and said heating body extractionelectrode each having high wettability for a low melting point metal.

A protection element according to another embodiment of the presentinvention comprises: an insulating substrate; a heating body builtinside the insulating substrate; first and second electrodes laminatedon the insulating substrate; a heating body extraction electrodeelectrically connected to the heating body on a current path between thefirst and second electrodes; and a fusible conductor laminated over arange from the heating body extraction electrode to the first and secondelectrodes, and fusing the current path between the first and secondelectrodes by heating of the heating body. Furthermore, the fusibleconductor comprises a layered body including at least a high meltingpoint metal layer and a low melting point metal layer. The low meltingpoint metal layer is melted by a heat generated by the heating body,whereby, while eroding the high melting point metal layer, the lowmelting point metal layer is drawn close to the side of the first andsecond electrodes and the heating body extraction electrode, and fused,said first and second electrodes and said heating body extractionelectrode each having high wettability for the low melting point metal.

A protection element according to another embodiment of the presentinvention comprises: an insulating substrate; a heating body laminatedon the insulating substrate; first and second electrodes laminated on asurface of the insulating substrate opposite to a surface thereof onwhich the heating body is laminated; a heating body extraction electrodeelectrically connected to the heating body on a current path between thefirst and second electrodes; and a fusible conductor laminated over arange from the heating body extraction electrode to the first and secondelectrodes, and fusing the current path between the first and secondelectrodes by heating of the heating body. Furthermore, the fusibleconductor comprises a layered body including at least a high meltingpoint metal layer and a low melting point metal layer. The low meltingpoint metal layer is melted by a heat generated by the heating body,whereby, while eroding the high melting point metal layer, the lowmelting point metal layer is drawn close to the side of the first andsecond electrodes and the heating body extraction electrode, and fused,said first and second electrodes and said heating body extractionelectrode each having high wettability for the low melting point metal.

A protection element according to another embodiment of the presentinvention comprises: an insulating substrate; a heating body laminatedon the insulating substrate; first and second electrodes laminated onthe same surface of the insulating substrate as a surface thereof onwhich the heating body is laminated; a heating body extraction electrodeelectrically connected to the heating body on a current path between thefirst and second electrodes; and a fusible conductor laminated over arange from the heating body extraction electrode to the first and secondelectrodes, and fusing the current path between the first and secondelectrodes by heating of the heating body. Furthermore, the fusibleconductor comprises a layered body including at least a high meltingpoint metal layer and a low melting point metal layer. The low meltingpoint metal layer is melted by a heat generated by the heating body,whereby, while eroding the high melting point metal layer, the lowmelting point metal layer is drawn close to the side of the first andsecond electrodes and the heating body extraction electrode, and fused,said first and second electrodes and said heating body extractionelectrode each having high wettability for the low melting point metal.

A protection element according to another embodiment of the presentinvention comprises: an insulating substrate; first and secondelectrodes laminated on the insulating substrate; a heating bodyextraction electrode laminated on a current path between the first andsecond electrodes; a heating element incorporated so as to beelectrically connected to the heating body extraction electrode; and afusible conductor laminated over a range from the heating bodyextraction electrode to the first and second electrodes, and fusing thecurrent path between the first and second electrodes by heating of theheating element. Furthermore, the fusible conductor comprises a layeredbody including at least a high melting point metal layer and a lowmelting point metal layer. The low melting point metal layer is meltedby a heat generated by the heating body melts, whereby, while erodingthe high melting point metal layer, the low melting point metal layer isdrawn close to the side of the first and second electrodes and theheating body extraction electrode, and fused, said first and secondelectrodes and said heating body extraction electrode each having highwettability for the low melting point metal.

A protection element according to another embodiment of the presentinvention comprises: an insulating substrate; a heating body laminatedon the insulating substrate; an insulating member laminated on theinsulating substrate so as to cover at least the heating body; first andsecond electrodes laminated on the insulating substrate having theinsulating member laminated thereon; a heating body extraction electrodeelectrically connected to the heating body on a current path between thefirst and second electrodes; and a fusible conductor laminated over arange from the heating body extraction electrode to the first and secondelectrodes, and fusing the current path between the first and secondelectrodes by heating. Furthermore, the fusible conductor is made of ahigh melting point metal and connected to each of the first electrode,the second electrode, and the heating body extraction electrode via alow melting point metal. The low melting point metal layer is melted bya heat generated by the heating body, whereby, while eroding the fusibleconductor made of the high melting point metal, the low melting pointmetal layer is drawn close to the side of the first and secondelectrodes and the heating body extraction electrode, and fused, saidfirst and second electrodes and said heating body extraction electrodeeach having high wettability for the low melting point metal.

Effects of Invention

In a protection element according to the present invention, when afusible conductor comprising a layered body including a high meltingpoint metal layer and a low melting point metal layer is heated, a heatgenerated by a heating body melts the low melting point metal layer,whereby, while eroding the high melting point metal layer, the lowmelting point metal layer is drawn close to the side of the first andsecond electrodes and the heating body extraction electrode, and fused,said first and second electrodes and said heating body extractionelectrode each having high wettability, and thus the fusing can besurely performed. Furthermore, it is clear that a protection elementaccording to the present invention has a fusible conductor and therebyalso functions as a usual current fuse, and can realize interruption ofboth a current path for an external signal and a current path for anovercurrent.

Furthermore, the low melting point metal layer is made of Pb-freesolder, meanwhile the high melting point metal layer is made of a metalcontaining Ag or Cu as a main component, and therefore, a demand forPb-free can be satisfied.

Since the volume of the low melting point metal layer is made largerthan the volume of the high melting point metal layer, the high meltingpoint metal layer can be effectively eroded.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a plan view of a protection element according to the presentinvention. FIG. 1B is a cross-sectional view of section A-A′ of FIG. 1A.

FIG. 2 is a block diagram illustrating an example of a protectionelement of the application of the present invention.

FIG. 3 illustrates an example of a circuit configuration of a protectionelement according to the present invention.

FIG. 4 is a cross-sectional view of a protection element of a knownexample (Japanese Patent Application Laid-Open No. 2004-185960).

FIGS. 5A-5B are schematic plan views for describing an operation of aprotection element according to the present invention. FIG. 5A is a planview illustrating a protection element before and just after anoperation thereof FIG. 5B is a plan view illustrating a state in which alow melting point metal layer in the vicinity of a heat source is meltedby a heating operation and is eroding a high melting point metal layer.FIG. 5C is a plan view illustrating a state in which erosion of the highmelting point metal layer is proceeding. FIG. 5D is a plan viewillustrating a state in which the low melting point metal layer has beendrawn close to electrodes and a heating body extraction electrode.

FIG. 6A is a plan view illustrating a modified example of the embodimentof a protection element according to the present invention. FIG. 6B is across-sectional view of section A-A′ of FIG. 6A.

FIG. 7A is a plan view illustrating another modified example of theembodiment of a protection element according to the present invention.FIG. 7B is a cross-sectional view of section A-A′ of FIG. 7A.

FIG. 8A is a plan view illustrating another modified example of theembodiment of a protection element according to the present invention.FIG. 8B is a cross-sectional view of section A-A′ of FIG. 8A.

FIGS. 9A-9D are schematic plan views for describing an operation of theprotection element according to the modified example of FIG. 8. FIG. 9Ais a plan view illustrating the protection element before and just afterthe operation thereof FIG. 9B is a plan view illustrating a state inwhich a low melting point metal layer in the vicinity of a heat sourceis melted by a heating operation and thereby is eroding a high meltingpoint metal layer. FIG. 9C is a plan view illustrating a state in whicherosion of the high melting point metal layer is proceeding. FIG. 9D isa plan view illustrating a state in which the low melting point metallayer has been drawn close to electrodes and a heating body extractionelectrode.

FIGS. 10A and 10B are perspective views illustrating examples of fusibleconductors, each having a different shape. FIG. 10A illustrates anexample of a fusible conductor having a rectangular parallelepiped shape(a cube shape), on the other hand, FIG. 10B illustrates an example of afusible conductor having a cylindrical shape.

FIG. 11A is a plan view illustrating another modified example of theembodiment of a protection element according to the present invention.FIG. 11B is a cross-sectional view of section A-A′ of FIG. 11A.

FIG. 12A is a plan view illustrating another modified example of theembodiment of a protection element according to the present invention.FIG. 12B is a cross-sectional view of section A-A′ of FIG. 12A.

FIG. 13A is a plan view illustrating another modified example of theembodiment of a protection element according to the present invention.FIG. 13B is a cross-sectional view of section A-A′ of FIG. 13A.

FIG. 14A is a plan view illustrating another modified example of theembodiment of a protection element according to the present invention.FIG. 14B is a cross-sectional view of section A-A′ of FIG. 14A.

FIG. 15A is a plan view illustrating another modified example of theembodiment of a protection element according to the present invention.FIG. 15B is a cross-sectional view of section A-A′ of FIG. 15A.

FIG. 16 is a cross-sectional view illustrating a modified example of aprotection element in which a heating body is built in an insulatingsubstrate.

FIG. 17 is a cross-sectional view illustrating a modified example of aprotection element in which a heating body is formed on a back surfaceof an insulating substrate.

FIG. 18 is a cross-sectional view illustrating a modified example of aprotection element in which a heating body is formed on a front surfaceof an insulating substrate.

FIG. 19 is a perspective view illustrating a modified example of aprotection element in which a heating element is mounted on a frontsurface of an insulating substrate.

FIGS. 20A and 20B illustrate a modified example of a protection elementusing a fusible conductor in which a linear opening portion is providedto a high melting point metal layer so that a low melting point metallayer is exposed therefrom, and FIG. 20A is a plan view thereof,meanwhile FIG. 20B is a cross-sectional view thereof.

FIGS. 21A and 21B illustrate a modified example of a protection elementusing a fusible conductor in which a circular opening portion isprovided to a high melting point metal layer so that a low melting pointmetal layer is exposed therefrom, and FIG. 21A is a plan view thereof,meanwhile FIG. 21B is a cross-sectional view thereof.

FIGS. 22A and 22B illustrate a modified example of a protection elementusing a fusible conductor in which a linear opening portion is providedto a high melting point metal layer so that a low melting point metallayer is exposed therefrom, and FIG. 22A is a plan view thereof,meanwhile FIG. 22B is a cross-sectional view thereof.

FIGS. 23A and 23B illustrate a modified example of a protection elementin which a fusible conductor having a two-layer structure comprising ahigh melting point metal layer and a low melting point metal layer isconnected by a low melting point metal, and FIG. 23A is a plan viewthereof, meanwhile FIG. 23B is a cross-sectional view thereof.

FIGS. 24A and 24B illustrate a modified example of a protection elementusing a fusible conductor having a four-layer structure in which highmelting point metal layers and low melting point metal layers arealternately laminated, and FIG. 24A is a plan view thereof, meanwhileFIG. 24B is a cross-sectional view thereof.

FIGS. 25A and 25B illustrate a modified example of a protection elementin which a fusible conductor composed of a monolayer of a high meltingpoint metal layer is connected by a low melting point metal, and FIG.25A is a plan view thereof, meanwhile FIG. 25B is a cross-sectional viewthereof.

FIG. 26 is a plan view illustrating a protection element in which aplurality of fusible conductors is provided and also an insulating layeris formed on a heating body extraction electrode.

FIG. 27 is a plan view illustrating a state in which, in a protectionelement provided with a plurality of fusible conductors and having aninsulating layer formed on a heating body extraction electrode, thefusible conductor has been fused.

FIG. 28 is a plan view illustrating a protection element in which aplurality of fusible conductors is provided and also a narrower portionis formed on a heating body extraction electrode.

FIG. 29 is a plan view illustrating a state in which, in a protectionelement provided with a plurality of fusible conductors and having anarrower portion formed on a heating body extraction electrode, thefusible conductor has been fused.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, an embodiment according to the present invention will bedescribed in detail with reference to the drawings. It should be notedthat the present invention is not limited only to the followingembodiment, and it is a matter of course that various changes can bemade within the scope not deviating from the gist of the presentinvention.

[Configuration of Protection Element]

As shown in FIG. 1, a protection element 10 according to the presentinvention comprises: an insulating substrate 11; a heating body 14laminated on the insulating substrate 11 and covered with an insulatingmember 15; electrodes 12(A1) and 12(A2) formed at both ends of theinsulating substrate 11; a heating body extraction electrode 16laminated on the insulating member 15 so as to be superimposed with theheating body 14; and a fusible conductor 13 each end of which isconnected to the corresponding one of electrodes 12 (A1) and 12 (A2) anda center portion of which is connected to the heating body extractionelectrode 16. Furthermore, external terminals connected to theelectrodes 12 (A1) and 12 (A2) are formed on a back surface of theinsulating substrate 11.

The insulating substrate 11 having a rectangular parallelepiped shape ismade of, for example, a material having insulating properties, such asalumina, glass ceramics, mullite, or zirconia. Besides, a material usedfor printed-circuit boards, such as a glass epoxy board and a phenolboard, may be used, but, it is necessary to care about a temperature forfusing.

The heating body 14 is made of an electrically-conductive material suchas W, Mo, or Ru, which has a comparatively high resistance and generatesheat when energized. The heating body 14 is formed in such a manner thata powder of an alloy, a composite, or a compound of the above-mentionedmaterial is mixed with a resin binder or the like to be made into apaste, and, with the obtained paste, a pattern is formed on theinsulating substrate 11 by screen printing technique, and baking isperformed.

The insulating member 15 is arranged so as to cover the heating body 14,and the heating body extraction electrode 16 is arranged so as to facethe heating body 14 via said insulating member 15. In order toefficiently conduct the heat of the heating body 14 to the fusibleconductor, the insulating member 15 may be laminated between the heatingbody 14 and the insulating substrate 11.

One end of the heating body extraction electrode 16 is connected to aheating body electrode 18(P1). Furthermore, one end of the heating body14 is connected to another heating body electrode 18(P2).

The fusible conductor 13 is a layered structure body comprising aninternal layer and an external layer, preferably has a high meltingpoint metal layer 13 a as the internal layer and a low melting pointmetal layer 13 b as the external layer. It should be noted that, asmentioned later, the fusible conductor 13 may have the low melting pointmetal layer 13 b as an internal layer and the high melting point metallayer 13 a as an external layer. Furthermore, the fusible conductor 13may have a two-layer structure body composed of an upper layer and alower layer, and may have the high melting point metal layer 13 a as theupper layer and the low melting point metal layer 13 b as the lowerlayer. The high melting point metal layer 13 a is preferably made of Agor Cu, or a metal containing any one of Ag and Cu as a main component,and has a melting point high enough not to melt even when a substrate ismounted by a reflow furnace. The low melting point metal layer 13 b ispreferably made of a metal containing Sn as a main component, the metalbeing a material generally called “Pb-free solder” (for example, M705,manufactured by Senju Metal Industry Co., Ltd.). The melting point ofthe low melting point metal layer 13 b does not necessarily need to behigher than the temperature of the reflow furnace, and the low meltingpoint metal layer 13 b may melt at approximately 200 degrees C.Lamination of the high melting point metal layer 13 a and the lowmelting point metal layer 13 b prevents the fusible conductor 13 frombeing fused even in the case where the reflow temperature exceeds amelting temperature of the low melting point metal layer 13 b, whereby alow melting point metal melts. The fusible conductor 13 may be formed byfilm-formation of the low melting point metal layer 13 b on the highmelting point metal layer 13 a, by using a plating technique.Alternatively, the fusible conductor 13 may be formed by laminating thelow melting point metal layer 13 b on the high melting point metal layer13 a, by using another well-known technique, such as a laminationtechnique or a film formation technique. Furthermore, on the contrary,also in the case where the high melting point metal layer 13 a is madeto serve as an external layer, the same film formation technique can beapplied to form the fusible conductor 13. It should be noted that solderjointing by using the low melting point metal layer 13 b allows thefusible conductor 13 to be connected to the heating body extractionelectrode 16 and the electrodes 12(A1) and 12(A2).

To prevent the low melting point metal layer 13 b serving as an externallayer from being oxidized, a flux 17 may be applied to almost the entiresurface of the fusible conductor 13.

To protect the inside of the protection element 10 having suchconfiguration, a cover member may be arranged on the insulatingsubstrate 11.

[Method for Use of Protection Element]

As shown in FIG. 2, the above-mentioned protection element 10 is usedfor a circuit in a battery pack of a lithium ion secondary battery.

For example, the protection element 10 is used by being incorporatedinto a battery pack 20 having a battery stack 25 comprising four batterycells 21 to 24 in total for a lithium ion secondary battery.

The battery pack 20 comprises: the battery stack 25; acharge-and-discharge control circuit 30 configured to control chargingand discharging of the battery stack 25; the protection element 10according to the present invention configured to interrupt charging atthe time of occurrence of abnormality in the battery stack 25;

a detection circuit 26 configured to detect the voltage of each of thebattery cells 21 to 24; and a current control element 27 configured tocontrol the operation of the protection element 10 depending on adetection result of the detection circuit 26.

The battery stack 25 comprises the battery cells 21 to 24 which areserially connected and require a control for protection from overchargeand overdischarge states, and the battery stack 25 is removablyconnected to a charging apparatus 35 via a positive electrode terminal20 a and a negative electrode terminal 20 b of the battery pack 20, anda charging voltage from the charging apparatus 35 is applied thereon.The positive electrode terminal 20 a and the negative electrode terminal20 b of the battery pack 20 charged by the charging apparatus 35 areconnected to an electronic device which operates with a battery, wherebythis electronic device can be operated.

The charge-and-discharge control circuit 30 comprises: two currentcontrol elements 31 and 32 which are serially connected in a currentpath flowing from the battery stack 25 to the charging apparatus 35; anda control unit 33 configured to control the operation of said currentcontrol elements 31 and 32. The current control elements 31 and 32 areconfigured with, for example, field-effect transistors (hereinafter,referred to as FET), and a gate voltage is controlled by the controlunit 33, whereby continuity and interruption of the current path of thebattery stack 25 are controlled. The control unit 33 operates inresponse to an electric power supply from the charging apparatus 35,and, depending on a detection result of the detection circuit 26, whenthe battery stack 25 is in an overdischarge state or in an overchargestate, the operations of the current control elements 31 and 32 arecontrolled so as to interrupt the current path.

The protection element 10 is, for example, connected on thecharge-and-discharge current path between the battery stack 25 and thecharge-and-discharge control circuit 30, and the operation of theprotection element 10 is controlled by the current control element 27.

The detection circuit 26 is connected to each of the battery cells 21 to24, and detects a voltage value of each of the battery cells 21 to 24 toprovide each of the voltage values to the control unit 33 of thecharge-and-discharge control circuit 30. Furthermore, the detectioncircuit 26 outputs a control signal to control the current controlelement 27 when any one of the battery cells 21 to 24 has an overchargevoltage or an overdischarge voltage.

The current control element 27 is configured with, for example, FET,and, when, based on a detection signal outputted from the detectioncircuit 26, it is detected that a voltage value of any of the batterycells 21 to 24 exceeds a predetermined overdischarge voltage or apredetermined overcharge voltage, the current control element 27operates the protection element 10 and controls so as to interrupt thecharge-and-discharge current path of the battery stack 25, not dependingon switching operation of the current control elements 31 and 32.

The configuration of the protection element 10 in the battery pack 20having the above-mentioned configuration will be specifically described.

First, the protection element 10 according to the present invention hasa circuit configuration as shown in FIG. 3, for example. That is, theprotection element 10 has a circuit configuration comprising: thefusible conductor 13 serially connected via the heating body extractionelectrode 16; and the heating body 14 configured to melt the fusibleconductor 13 by heat generation caused by passing current connectingpoints to the fusible conductor 13. Furthermore, in the protectionelement 10, for example, the fusible conductor 13 is serially connectedon a charge-and-discharge current path, and the heating body 14 isconnected to the current control element 27. One of the two electrodes12 of the protection element 10 is connected to A1, meanwhile the otherone is connected to A2. Furthermore, the heating body extractionelectrode 16 and one of the heating body electrodes 18 connected to saidheating body extraction electrode 16 are connected to P1, meanwhileanother one of the heating body electrodes 18 is connected to P2.

The protection element 10 having such circuit configuration is shorterin height and Pb-free, meanwhile the protection element 10 can surelyfuse the fusible conductor 13 on a current path by heat generation ofthe heating body 14.

It should be noted that the protection element according to the presentinvention can be not only used for a battery pack of a lithium ionsecondary battery, but also applied to various uses requiringinterruption of a current path by an electric signal.

[Operation of Protection Element]

First, for a comparison, a known example (Japanese Patent ApplicationLaid-Open No. 2004-185960) will be taken up as an example of aconventional protection element to describe the configuration thereof.

As shown in FIG. 4, in a protection element 40 according to the priorart, a glass layer 41 a is formed as an insulating base layer on arectangular substrate 41, and a heating body 44 is laminated on theglass layer 41 a. An insulating member 45 is formed so as to cover theheating body 44, and a high melting point metal layer 43 a is laminatedso as to face the heating body 44 via the insulating member 45, and,furthermore, a low melting point metal layer 43 b is laminated thereon.Electrodes 42 are laminated at and connected to both ends of the highmelting point metal layer 43 a and the low melting point metal layer 43b so as to be sandwiched between the high melting point metal layer 43 aand the low melting point metal layer 43 b. A flux 47 is applied on thelow melting point metal layer 43 b.

As mentioned above, in the protection element 40 according to the priorart, the whole of the high melting point metal layer 43 a is formed soas to directly come into full contact with the insulating member 45. Inthis configuration, circuit interruption is performed only by an actionin which the low melting point metal layer 43 b is melted by heatgeneration of the heating body 44, and thereby erodes the high meltingpoint metal layer 43 a. Even if the interruption is not perfectly done,at the time when the fusible conductor has a high resistance, thepassage of a current to the heating body 44 is controlled, whereby theheat generation is stopped. In other words, sometimes the circuit cannotbe perfectly interrupted.

In the protection element 10 according to the present invention as shownin FIG. 1, the high melting point metal layer 13 a and the low meltingpoint metal layer 13 b are connected to the heating body extractionelectrode 16 and the electrode 12 so as to straddle a space between theheating body extraction electrode 16 and the electrode 12. Therefore, inaddition to an action of eroding the high melting point metal layer bymelting the low melting point metal layer 13 b, a physical extractionaction caused by surface tension of the molten low melting point metallayer 13 b on each of the connected electrodes 12 allows the fusibleconductor 13 to be surely fused.

Hereinafter, the operation of the protection element 10 according to thepresent invention will be described.

FIGS. 5A-5D schematically illustrate how the fusible conductor 13 actswhen a current is made to pass through the heating body 14 of theprotection element 10 as shown in FIG. 1.

FIG. 5A illustrates a state before passing a current through the heatingbody 14 and at the beginning of the start of said passage of a currentby connecting a power source so as to apply a voltage between theheating body electrode 18(P2) and the electrodes 12(A1), (A2). Theresistance of the heating body 14 is preferably set according to anapplied voltage so that the temperature of heat generated by the heatingbody 14 is higher than a usual reflow temperature (not more than 260degrees C.), that is, not less than 300 degrees C.

As shown in FIG. 5B, the low melting point metal layer 13 b as anexternal layer of the fusible conductor 13 arranged right above theheating body 14 starts melting, and the molten low melting point metaldiffuses into the high melting point metal layer 13 a serving as aninternal layer, whereby an erosion phenomenon is caused and the highmelting point metal layer 13 a is eroded and disappears. Inside thecircle with broken line, there is a state in which the high meltingpoint metal layer 13 a has disappeared and been mingled with the moltenlow melting point metal layer 13 b.

As shown in FIG. 5C, the temperature of the heating body 14 furtherrises, whereby there is expanded an area of the high melting point metallayer 13 a eroded by melting of the low melting point metal layer 13 bserving as an external layer of the fusible conductor 13. In this state,adoption of a metal having a high thermal conductivity as a material ofthe high melting point metal layer 13 a allows an area including theelectrodes 12 to have a high temperature, whereby the whole of the lowmelting point metal layer 13 b is in a molten state. At this time, whenthe high melting point metal layer 13 a is completely eroded on theheating body extraction electrode 16, the low melting point metal layer13 b, that is, solder is drawn closed to each of the heating bodyextraction electrode 16 and the two electrodes 12(A1) and 12(A2) becauseof its wettability (surface tension), as shown in FIG. 5D. As a result,interruption between each of the electrodes is completed.

MODIFIED EXAMPLE 1

As shown in FIG. 6, a protection element 50 of a modified exampleaccording to the present invention comprises: an insulating substrate11; a heating body 14 laminated on the insulating substrate 11 andcovered with an insulating member 15; electrodes 12(A1) and 12(A2)formed at both ends of the insulating substrate 11; a heating bodyextraction electrode 16 laminated on the insulating member 15 so as tobe superimposed with the heating body 14; and a fusible conductor 13each end of which is connected to the corresponding one of electrodes 12(A1) and 12 (A2) and a center portion of which is connected to theheating body extraction electrode 16. Furthermore, external terminalsconnected to the electrodes 12(A1) and 12(A2) are formed on a backsurface of the insulating substrate 11.

In the case of a fusible conductor which uses common higher meltingpoint solder (Pb-containing solder), the fusible conductor has a lowthermal conductivity, and therefore, the temperatures of electrodeportions at both ends of the protection element cannot reach a meltingtemperature in a short time. On the other hand, in the case of thefusible conductor in the protection element according to the presentinvention, the fusible conductor having a high melting point metal layermade of Ag or Cu, or a metal containing any one of Ag and Cu as a maincomponent, the fusible conductor has a high thermal conductivity, andtherefore, in order that also the temperatures of electrode portions atboth ends of the protection element sufficiently reach a meltingtemperature of a low melting point metal layer, a solder accumulationportion mentioned later is provided so that more stable fusioncharacteristics can be achieved.

The fusible conductor 13 is a layered structure body comprising aninternal layer and an external layer, preferably has a high meltingpoint metal layer 13 a as an internal layer and a low melting pointmetal layer 13 b as an external layer. Alternatively, the fusibleconductor 13 may have the low melting point metal layer 13 b as aninternal layer and the high melting point metal layer 13 a as anexternal layer. The high melting point metal layer 13 a is preferablymade of Ag or Cu, or a metal containing any one of Ag and Cu as a maincomponent, and preferably has a melting point high enough not to melteven when a substrate is mounted by a reflow furnace. The low meltingpoint metal layer 13 b is preferably made of a metal containing Sn as amain component, the metal being a material generally called “Pb-freesolder” (for example, M705, manufactured by Senju Metal Industry Co.,Ltd.). The melting point of the low melting point metal layer 13 b doesnot necessarily need to be higher than the temperature of the reflowfurnace, and the low melting point metal layer 13 b may melt atapproximately 200 degrees C. The fusible conductor 13 may be formed byfilm-formation of the low melting point metal layer 13 b on the highmelting point metal layer 13 a by using plating technique.Alternatively, the fusible conductor 13 may be formed by laminating thelow melting point metal layer 13 b on the high melting point metal layer13 a by using another well-known lamination technique or film formationtechnique. Furthermore, on the contrary, also in the case where the highmelting point metal layer 13 a is made to serve as an external layer,the same film formation technique can be applied to form the fusibleconductor 13.

Here, solder accumulation portions 51 made of the same material as thelow melting point metal layer 13 b are provided at both ends of thefusible conductor 13 to which the electrodes 12(A1) and 12(A2) areconnected. At the time of an operation of the protection element, thelow melting point metal layer 13 b including the accumulation portions51 is in a fully molten state. When the high melting point metal layer13 a is eroded in the whole of the fusible conductor 13, the moltenfusible conductor 13 is easily drawn close to each of the accumulationportions 51 and 51 at the corresponding one of the electrodes 12(A1) and12(A2), whereby the fusible conductor can be more surely fused.

MODIFIED EXAMPLE 2

As shown in FIG. 7, a protection element 60 comprises: an insulatingsubstrate 11; a heating body 14 laminated on the insulating substrate 11and covered with an insulating member 15; electrodes 12(A1) and 12(A2)formed at both ends of the insulating substrate 11; a heating bodyextraction electrode 16 laminated on the insulating member 15 so as tobe superimposed with the heating body 14; and a fusible conductor 13each end of which is connected to the corresponding one of electrodes12(A1) and 12(A2) and a center portion of which is connected to theheating body extraction electrode 16. Furthermore, external terminalsconnected to the electrodes 12(A1) and 12(A2) are formed on a backsurface of the insulating substrate 11.

The fusible conductor 13 is a layered structure body comprising aninternal layer and an external layer, preferably having a high meltingpoint metal layer 13 a as an internal layer and a low melting pointmetal layer 13 b as an external layer. As the above-mentioned modifiedexample, accumulation portions 51 and 51 may be provided at both ends ofthe fusible conductor 13.

In this modified example, many openings 61 are provided to the highmelting point metal layer 13 a, and the low melting point metal layer 13b is film-formed on said high melting point metal layer 13 a having themany openings, for example, by using a plating technique. Thus, the areaof the high melting point metal layer 13 a which comes in contact withthe low melting point metal layer 13 b to be melted is increased, andaccordingly the low melting point metal layer 13 b can erode the highmelting point metal layer 13 a in a shorter time.

Therefore, the fusible conductor can be more quickly and surely fused.

MODIFIED EXAMPLE 3

FIG. 8 illustrates another modified example wherein the configuration ofthe above-mentioned fusible conductor 13 was modified.

As shown in FIG. 8, a protection element 70 comprises: an insulatingsubstrate 11; a heating body 14 laminated on the insulating substrate 11and covered with an insulating member 15; electrodes 12(A1) and 12(A2)formed at both ends of the insulating substrate 11; a heating bodyextraction electrode 16 laminated on the insulating member 15 so as tobe superimposed with the heating body 14; and a fusible conductor 13each end of which is connected to the corresponding one of electrodes12(A1) and 12(A2) and a center portion of which is connected to theheating body extraction electrode 16. Furthermore, external terminalsconnected to the electrodes 12(A1) and 12(A2) are formed on a backsurface of the insulating substrate 11.

The fusible conductor 13 comprises a low melting point metal layer 13 bas an internal layer and a high melting point metal layer 13 a as anexternal layer. As mentioned above, Pb-free solder containing Sn as amain component may be used for the low melting point metal layer 13 b,meanwhile Ag or Cu, or a metal containing any one of Ag and Cu as a maincomponent may be used for the high melting point metal layer 13 a. Inthe case of the modified example of FIG. 8, a flux 17 is applied on thefusible conductor 13 in order to prevent a melting temperature fromrising due to oxidization of a surface of the fusible conductor 13 andalso to maintain the surface tension of solder which is in aheat-generating and melting state.

As is the case with the configuration example shown in FIG. 1, a platingtechnique is applied to the low melting point metal layer 13 b as aninternal layer to form the high melting point metal layer 13 a as anexternal layer, whereby the fusible conductor 13 in this modifiedexample can be formed.

FIGS. 9A-9D schematically illustrate an operation of the configurationexample shown in FIG. 8.

FIG. 9A illustrates a state before passing a current through the heatingbody 14 and at the beginning of the start of said passage of a currentby connecting a power source so as to apply a voltage between theheating body electrode 18(P2) and the electrodes 12(A1), (A2).

As shown in FIG. 9B, the low melting point metal layer 13 b serving asan internal layer of the fusible conductor 13 right above the heatingbody 14 starts melting, and then the erosion phenomenon causes the lowmelting point metal to diffuse into the high melting point metal layer13 a as an external layer. Thus, the high melting point metal layer 13 aas an external layer is eroded and disappears, meanwhile the low meltingpoint metal layer 13 b as an internal layer begins to be exposed. Theinterior of a circle with a solid line in the figure represents theexposed low melting point metal layer 13 b, meanwhile the exterior ofthe circle represents the high melting point metal layers 13 a as anexternal layer.

As shown in FIG. 9C, the temperature of the heating body 14 furtherrises, whereby melting of the low melting point metal layer 13 b as aninternal layer of the fusible conductor 13 proceeds, and thus an area oferoding the high melting point metal layer 13 a is expanded. At thistime, the whole of the low melting point metal layer 13 b is in a moltenstate, and therefore, when the high melting point metal layer 13 a iscompletely eroded on the heating body extraction electrode 16, the lowmelting point metal layer 13 b, that is, solder is drawn close to eachof the heating body extraction electrode 16 and the two electrodes 12(A1) and 12 (A2) because of its wettability (surface tension), as shownin FIG. 9D. As a result, interruption between each of the electrodes iscompleted.

The fusible conductor 13 may be a fusible conductor having a rectangularparallelepiped shape as shown in FIG. 10A, or may be a fusible conductorhaving a cylindrical shape as shown in FIG. 10B. In FIGS. 10A and 10B,the low melting point metal layer 13 b serves as an internal layer,meanwhile the high melting point metal layer 13 a serves as an externallayer, but, of course, on the contrary, the low melting point metallayer 13 b may serve as an external layer, meanwhile the high meltingpoint metal layer 13 a may serve as an internal layer.

Also in the case where the low melting point metal layer 13 b serves asan internal layer, meanwhile the high melting point metal layer 13 aserves as an external layer, accumulation portions composed of a lowmelting point metal layer 13 b being thicker than the low melting pointmetal layer 13 b of the fusible conductor 13 may be provided on theelectrodes 12(A1) and 12(A2), with care to maintain the thickness of thefusible conductor 13.

MODIFIED EXAMPLE 4

FIG. 11 illustrates another modified example wherein the configurationof the fusible conductor 13 was modified.

As shown in FIG. 11, a protection element 80 comprises: an insulatingsubstrate 11; a heating body 14 laminated on the insulating substrate 11and covered with an insulating member 15; electrodes 12(A1) and 12(A2)formed at both ends of the insulating substrate 11; a heating bodyextraction electrode 16 laminated on the insulating member 15 so as tobe superimposed with the heating body 14; and a fusible conductor 13each end of which is connected to the corresponding one of electrodes12(A1) and 12(A2) and a center portion of which is connected to theheating body extraction electrode 16. Furthermore, external terminalsconnected to the electrodes 12(A1) and 12(A2) are formed on a backsurface of the insulating substrate 11.

The fusible conductor 13 has a two-layer structure comprising a lowmelting point metal layer 13 b as a lower layer and a high melting pointmetal layer 13 a as an upper layer. As is the case mentioned above,Pb-free solder containing Sn as a main component may be used for the lowmelting point metal layer 13 b, meanwhile Ag or Cu, or a metalcontaining any one of Ag and Cu as a main component may be used for thehigh melting point metal layer 13 a.

In the case of the modified example of FIG. 11, in order to control theerosion of the electrodes themselves by the low melting point metallayer 13 b and thereby to improve fusion characteristics, a platingtreatment is applied to surfaces of the external terminals connected tothe two electrodes 12 and 12, and a surface of the heating bodyextraction electrode 16, and thus a Ni/Au plating layer 52 is thusformed thereon. It should be noted that, in place of Ni/Au plating, aknown plating treatment, such as Ni/Pd plating or Ni/Pd/Au plating, maybe used.

MODIFIED EXAMPLE 5

FIG. 12A and FIG. 12B illustrate another modified example wherein theconfiguration of the fusible conductor is further modified.

A fusible conductor 91 of a protection element 90 shown in FIG. 12 is alayered structure body comprising an internal layer and an externallayer, and has a low melting point metal layer 91 b as an internal layerand a high melting point metal layer 91 a as an external layer.Furthermore, in the fusible conductor 91 of the protection element 90,the entire surface of the low melting point metal layer 91 b is coatedwith the high melting point metal layer 91 a.

Said fusible conductor 91 can be formed, for example, in such a mannerthat a sheet made of Pb-free solder containing Sn as a main component islaminated on, or a paste of Pb-free solder containing Sn as a maincomponent is applied to a sheet made of a high melting point metal, suchas Ag, and, furthermore, a high melting point metal sheet is laminatedthereon and heat-pressed. Alternatively, the fusible conductor 91 can beformed by applying Ag plating to the entire surface of a sheet made ofPb-free solder.

This fusible conductor 91 is connected onto an electrode 12 and aheating body extraction electrode 16 via a low melting point metal 92,such as Pb-free solder. Furthermore, a flux 17 is applied to almostwhole of the top surface of the fusible conductor 91. It should be notedthat, in order to control the erosion of the electrode itself andthereby to improve fusion characteristics, a Ni/Pd/Au plating layer 93is formed on a surface of the electrode 12 and the heating bodyextraction electrode 16.

In the protection element 90, even in the case where a low melting pointmetal layer 91 b having a melting point lower than a reflow temperatureis used, the use of the fusible conductor 91 in which the entire surfaceof the low melting point metal layer 91 b as an internal layer is coatedwith the high melting point metal layer 91 a as an external layer allowsan outflow of the low melting point metal layer 91 b as the internallayer toward the exterior to be controlled at the time of reflowmounting. Therefore, the protection element 90 allows the low meltingpoint metal layer 91 b to erode the high melting point metal layer 91 ain a shorter time by using a heat generated by the heating body 14,whereby the fusible conductor 91 can be more quickly and surely fused.

Furthermore, the protection element 90 can control an outflow of the lowmelting point metal layer 91 b as an internal layer at the time ofreflow mounting, and thereby control deformation of the fusibleconductor 91.

MODIFIED EXAMPLE 6

FIG. 13A and FIG. 13B illustrate another modified example wherein theconfiguration of connecting the fusible conductor 91 to the electrode 12and the heating body extraction electrode 16, each being shown in FIG.12, is modified.

In a protection element 100 shown in FIG. 13, a fusible conductor 91 isconnected to the electrode 12 and the heating body extraction electrode16 by an electrically conductive paste 95. For the electricallyconductive paste 95, a metal nano-paste, such as a silver nano-paste, ispreferably used. A silver nano paste forms a high melting point metalfilm at a baking temperature of not less than 200 degrees C., that is,approximately a reflow temperature. Furthermore, a baked film made of asilver nano-paste has conductivity and thermal conductivity which areinferior by approximately 50% to those of bulk silver.

In the protection element 100, the fusible conductor 91 is connected byusing the electrically conductive paste 95 made of such metalnano-paste, and therefore, at the time of reflow mounting, theelectrically conductive paste 95 is baked to form a metallic film,whereby erosion of a high melting point metal layer 91 a constituting anexternal layer of the fusible conductor 91 can be controlled. That is,in the case where the fusible conductor 91 is connected by a low meltingpoint metal, such as solder, the solder is melted at the time of reflowmounting, thereby eroding the high melting point metal layer 91 a as anexternal layer, and therefore the high melting point metal layer 91 a asan external layer needs to be thickly formed. However, if the highmelting point metal layer 91 a is thickly formed, it takes more time tofuse the fusible conductor 91.

On the other hand, in the protection element 100, the fusible conductor91 is connected by using the electrically conductive paste 95 made of ametal nano-paste, and therefore the high melting point metal layer 91 aas an external layer is not eroded, and accordingly the high meltingpoint metal layer 91 a can be thinly formed. Therefore, the protectionelement 100 allows the fusible conductor 91 to be surely fused in ashorter time by erosion by the low melting point metal layer 91 b as aninternal layer.

It should be noted that, in the protection element 100, besides thefusible conductor 91 shown in FIG. 12 in which the entire surface of thelow melting point metal layer 91 b as an internal layer is coated withthe high melting point metal layer 91 a, there may be used the fusibleconductor 13 shown in FIG. 8 in which the high melting point metal layer13 a is laminated on only the top and the bottom surfaces of the lowmelting point metal layer 13 b as an internal layer and said low meltingpoint metal layer 13 b is not completely coated therewith.

MODIFIED EXAMPLE 7

FIG. 14A and FIG. 14B illustrate another modified example wherein theconfiguration of connecting the fusible conductor 13 to the electrode 12and the heating body extraction electrode 16, each being shown in FIG.8, is modified.

In a protection element 110 shown in FIG. 14, a fusible conductor 13 isconnected to an electrode 12 and a heating body extraction electrode 16by ultrasonic welding or the like. As shown in FIG. 8, the fusibleconductor 13 is such that a high melting point metal layer 13 a islaminated on only the top and the bottom surfaces of a low melting pointmetal layer 13 b as an internal layer and thus said low melting pointmetal layer 13 b is not completely coated therewith.

In the protection element 110, an Ag plating layer is preferably formedas the high melting point metal layer 13 a of the fusible conductor 13,meanwhile a Ni/Pd/Au plating layer 93 is preferably formed on thesurfaces of the electrode 12 and the heating body extraction electrode16. Adhesion by welding between Ag and Ag and between Ag and Au isexcellent, and therefore, in the protection element 110, the fusibleconductor 13 can be surely connected to the electrode 12 and the heatingbody extraction electrode 16. Furthermore, in the protection element110, the fusible conductor 13 is connected to the electrode 12 and theheating body extraction electrode 16 by welding, and therefore the highmelting point metal layer 13 a of the fusible conductor 13 is not erodeddue to reflow mounting, and accordingly, compared with the case wherethe fusible conductor 13 is connected by using a low melting pointmetal, such as solder, the high melting point metal layer 13 a can bemore thinly formed. Thus, the protection element 110 allows the fusibleconductor 13 to be surely fused in a shorter time by erosion by the lowmelting point metal layer 13 b as an internal layer.

It should be noted that, in the protection element 110, besides thefusible conductor 13 shown in FIG. 14 in which the high melting pointmetal layer 13 a is laminated on only the top and the bottom surfaces ofthe low melting point metal layer 13 b as an internal layer and said lowmelting point metal layer 13 b is not completely coated therewith, theremay be used the fusible conductor 91 shown in FIG. 12 in which theentire surface of the low melting point metal layer 91 b as an internallayer is coated with the high melting point metal layer 91 a.

MODIFIED EXAMPLE 8

FIG. 15 illustrates another modified example wherein the configurationof the fusible conductor was further modified.

A fusible conductor 121 of a protection element 120 shown in FIG. 15 issuch that the entire surface of a low melting point metal layer 121 b asan internal layer is coated with a high melting point metal layer 121 a,and the entire surface of said high melting point metal layer 121 a iscoated with a second low melting point metal layer 121 c. The furthercoating of the high melting point metal layer 121 a as an external layerwith the second low melting point metal layer 121 c in the fusibleconductor 121 can prevent oxidization of Cu even in the case, forexample, where a Cu plating layer is formed as the high melting pointmetal layer 121 a. Therefore, the fusible conductor 121 can prevent afusion time from being longer due to oxidization of Cu, thereby allowingfusing to be performed in a shorter time.

Furthermore, in the fusible conductor 121, a metal which is inexpensivebut easily oxidized, such as Cu, can be used as the high melting pointmetal layer 121 a, and thus the fusible conductor 121 can be formedwithout using an expensive material, such as Ag.

The same material as that for the low melting point metal layer 121 b asan internal layer may be used for the second low melting point metallayer 121 c, and, for example, Pb-free solder containing Sn as a maincomponent may be used. Furthermore, the second low melting point metallayer 121 c may be formed by applying Sn plating to the surface of thehigh melting point metal layer 121 a.

It should be noted that, in the fusible conductor 121, the entiresurface of the low melting point metal layer 121 b as an internal layermay be coated with the high melting point metal layer 121 a, oralternatively, the high melting point metal layer 121 a may be laminatedon only the top and the bottom surfaces of the low melting point metallayer 121 b serving as an internal layer and thus said low melting pointmetal layer 121 b may be not completely coated therewith. Similarly, inthe fusible conductor 121, the entire surface of the high melting pointmetal layer 121 a may be coated with the second low melting point metallayer 121 c, or alternatively, the second low melting point metal layer121 c may be laminated on only the top and the bottom surfaces of thehigh melting point metal layer 121 a and thus said high melting pointmetal layer 121 a may be not completely coated therewith.

MODIFIED EXAMPLE 9

A fusible conductor 13 of the protection element to which the presentinvention is applied has a coating structure comprising a low meltingpoint metal layer 13 b as an internal layer and a high melting pointmetal layer 13 a as an external layer, and a layer thickness ratio ofthe low melting point metal layer 13 b to the high melting point metallayer 13 a may be from 2.1:1 to 100:1. Thus, the low melting point metallayer 13 b can surely have a volume larger than the high melting pointmetal layer 13 a has, whereby fusing by erosion of the high meltingpoint metal layer 13 a can be effectively performed in a shorter time.

In other words, in the fusible conductor, the high melting point metallayer 13 a is laminated on the top and bottom surfaces of the lowmelting point metal layer 13 b constituting an internal layer, andtherefore, the thicker the low melting point metal layer 13 b is than alayer thickness ratio of the low melting point metal layer to the highmelting point metal layer of 2.1:1, the larger volume the low meltingpoint metal layer 13 b can have than the high melting point metal layer13 a has. Furthermore, in the fusible conductor, in the case where alayer thickness ratio of the low melting point metal layer to the highmelting point metal layer is more than 100:1, and thus the low meltingpoint metal layer 13 b is thicker meanwhile the high melting point metallayer 13 a is thinner with respect to said layer thickness ratio, thereis a risk that the high melting point metal layer 13 a might be erodedby the low melting point metal layer 13 b melted by a heat generated atthe time of reflow mounting.

As for the range of said layer thickness ratio, a plurality of samplesof fusible conductors each having a different layer thickness ratio isprepared, and arranged on an electrode 12 and a heating body extractionelectrode 16 via a solder paste, then fed into a reflow furnace; andthen it is observed whether an fusible conductor is fused or not. As aresult, it was confirmed that, in the case where a layer thickness ratioof the low melting point metal layer to the high melting point metallayer was within a range of from 2.1:1 to 100:1, the fusible conductorwas not fused even at the time of reflow mounting, and in addition tothis, heating by the heating body 14 allows the high melting point metallayer 13 a to be eroded by the low melting point metal layer 13 b,whereby the fusible conductor was quickly fused.

It should be noted that also the fusible conductor 91 in which theentire surface of the low melting point metal layer 91 b as an internallayer is coated by the high melting point metal layer 91 a may have thesame layer thickness ratio of the low melting point metal layer to thehigh melting point metal layer as that of the above-mentioned fusibleconductor 13. Said layer thickness ratio allows the low melting pointmetal layer 13 b to have a larger volume than the high melting pointmetal layer 13 a has even in the case where the fusible conductor 91 isused, whereby fusing by erosion of the high melting point metal layer 13a can be effectively performed in a shorter time.

MODIFIED EXAMPLE 10

FIG. 16 illustrates another modified example wherein the arrangementposition of the heating body 14 is changed. As shown in FIG. 16, aprotection element 130 comprises: an insulating substrate 11; a heatingbody 14 built in the insulating substrate 11; electrodes 12(A1) and12(A2) formed at both ends of the insulating substrate 11; a heatingbody extraction electrode 16 laminated on the insulating substrate 11 soas to be superimposed with the heating body 14; and a fusible conductor13 each end of which is connected to the corresponding one of electrodes12(A1) and 12(A2) and a center portion of which is connected to theheating body extraction electrode 16. The protection element 130 has thesame configuration as the above-mentioned protection element 80 has,except that the heating body 14 is built in the insulating substrate 11and the insulating member 15 is not provided.

It should be noted that external terminals 131 connected to theelectrodes 12(A1) and 12(A2) are formed on a back surface 11 b of theinsulating substrate 11. Moreover, a cover member 132 to protect a frontsurface of the insulating substrate 11 is provided in the protectionelement 130.

The fusible conductor 13 has a two layer structure comprising a highmelting point metal layer 13 a as an upper layer and a low melting pointmetal layer 13 b as a lower layer, and is connected to the electrodes12(A1) and 12(A2) and the heating body extraction electrode 16, saidelectrodes 12(A1) and 12(A2) and said heating body extraction electrode16 being provided with a Ni/Au plating layer 52, via said low meltingpoint metal layer 13 b. Furthermore, in the fusible conductor 13, a flux17 is applied on a front surface of the high melting point metal layer13 a.

In this protection element 130, the heating body 14 is built in theinsulating substrate 11, whereby a front surface 11 a of the insulatingsubstrate 11 is made flat, and thus the heating body extractionelectrode 16 can be formed on the same plane as the electrodes 12(A1)and 12(A2). Furthermore, in this protection element 130, the heatingbody extraction electrode 16 is made to have the same height as theelectrodes 12(A1) and 12(A2) have, whereby the fusible conductor 13 canbe made flat to be connected thereto. Therefore, in the protectionelement 130, fusion characteristics of the fusible conductor 13 can beimproved.

Furthermore, in the protection element 130, a material excellent inthermal conductivity is used for the insulating substrate 11, whereby,as is the case where the fusible conductor 13 is heated via aninsulating member 15, such as a glass layer, the fusible conductor 13can be heated by the heating body 14.

Furthermore, in the protection element 130, an insulating member 15 isunnecessary, and an electrically conductive paste to constitute theelectrodes 12(A1) and 12(A2) and the heating body extraction electrode16 is applied to the front surface 11 a of the flat insulating substrate11, whereby the electrodes 12(A1) and 12(A2) and the heating bodyextraction electrode 16 can be collectively formed, and thus thereduction of labor in a manufacturing process can be achieved.

MODIFIED EXAMPLE 11

FIG. 17 illustrates another modified example wherein the arrangementposition of the heating body 14 is changed.

As shown in FIG. 17, a protection element 140 comprises: an insulatingsubstrate 11; a heating body 14 laminated on a back surface 11 b of theinsulating substrate 11 and coated with an insulating member 15;electrodes 12(A1) and 12(A2) formed at both ends of the insulatingsubstrate 11; a heating body extraction electrode 16 laminated on theinsulating substrate 11 so as to be superimposed with the heating body14; and a fusible conductor 13 each end of which is connected to thecorresponding one of electrodes 12(A1) and 12(A2) and a center portionof which is connected to the heating body extraction electrode 16. Theprotection element 140 has the same configuration as the above-mentionedprotection element 80 has, except that the heating body 14 is laminatedon the back surface 11 b of the insulating substrate 11.

It should be noted that external terminals 131 connected to theelectrodes 12(A1) and 12(A2) are formed on a back surface 11 b of theinsulating substrate 11. Moreover, a cover member 132 to protect thefront surface of the insulating substrate 11 is provided in theprotection element 140.

In this protection element 140, the heating body 14 is laminated on theback surface 11 b of the insulating substrate 11, whereby a frontsurface 11 a of the insulating substrate 11 is made flat, and thus theheating body extraction electrode 16 can be formed on the same plane asthe electrodes 12(A1) and 12(A2). Furthermore, in this protectionelement 100, the heating body extraction electrode 16 has the sameheight as the electrodes 12 (A1) and 12 (A2) have, whereby the fusibleconductor 13 can be made flat to be connected. Therefore, in theprotection element 100, fusion characteristics of the fusible conductor13 can be improved.

Furthermore, in the protection element 140, a material excellent inthermal conductivity is used for the insulating substrate 11, wherebythe fusible conductor 13 can be heated by the heating body 14, as is thecase where a heating body 14 is laminated on the front surface 11 a ofthe insulating substrate 11.

Furthermore, in the protection element 140, an electrically conductivepaste to constitute the electrodes 12(A1) and 12(A2) and the heatingbody extraction electrode 16 is applied to the front surface 11 a of theflat insulating substrate 11, whereby the electrodes 12(A1) and 12(A2)and the heating body extraction electrode 16 can be collectively formed,and thus the reduction of labor in a manufacturing process can beachieved.

MODIFIED EXAMPLE 12

FIG. 18 illustrates another modified example wherein the arrangementposition of the heating body 14 is changed.

As shown in FIG. 18, a protection element 150 comprises: an insulatingsubstrate 11; a heating body 14 laminated on a front surface 11 a of theinsulating substrate 11 and coated with an insulating member 15;electrodes 12(A1) and 12(A2) formed on the front surface 11 a of theinsulating substrate 11 so as to be adjacent to the heating body 14; aheating body extraction electrode 16 laminated between the electrodes12(A1) and 12(A2) on the front surface 11 a of the insulating substrate11 and electrically connected to the heating body 14; and a fusibleconductor 13 each end of which is connected to the corresponding one ofelectrodes 12(A1) and 12(A2) and a center portion of which is connectedto the heating body extraction electrode 16. The protection element 150has the same configuration as the above-mentioned protection element 80has, except that the heating body 14 is laminated on the front surface11 a of the insulating substrate 11.

It should be noted that external terminals 131 connected to theelectrodes 12(A1) and 12(A2) are formed on a back surface 11 b of theinsulating substrate 11. Moreover, a cover member 132 to protect thefront surface of the insulating substrate 11 is provided in theprotection element 150.

In this protection element 150, the heating body 14 is laminated on thefront surface 11 a of the insulating substrate 11 so as to be adjacentto the electrode 12(A1), whereby the front surface 11 a of theinsulating substrate 11 is made flat, and thus the heating bodyextraction electrode 16 can be formed on the same plane as theelectrodes 12(A1) and 12(A2). Furthermore, in the protection element150, the heating body extraction electrode 16 has the same height as theelectrodes 12(A1) and 12(A2) have, whereby the fusible conductor 13 canbe made flat to be connected thereto. Therefore, in the protectionelement 150, fusion characteristics of the fusible conductor 13 can beimproved.

Furthermore, in the protection element 150, the heating body 14 islaminated so as to be adjacent to the electrode 12(A1), whereby agenerated heat can be efficiently transferred to the fusible conductor13, and thus the fusible conductor 13 can be heated as is the case wherethe heating body 14 is superimposed with the heating body extractionelectrode 16 via the insulating member 15.

Furthermore, in the protection element 150, an electrically conductivepaste to constitute the electrodes 12(A1) and 12(A2), the heating body14, and the heating body extraction electrode 16 is applied to the frontsurface 11 a of the flat insulating substrate 11, whereby the electrodes12(A1) and 12(A2), the heating body 14, and the heating body extractionelectrode 16 can be collectively formed, and thus the reduction of laborin a manufacturing process can be achieved. Furthermore, in theprotection element 110, the heating body 14 is formed on the frontsurface 11 a of the insulating substrate 11 and not superimposed withthe heating body extraction electrode 16, and therefore the protectionelement 110 can be miniaturized by the height reduction in a thicknessdirection of the insulating substrate 11.

MODIFIED EXAMPLE 13

FIG. 19 illustrates another modified example wherein, in place ofapplying the configuration in which a heating element 14 is formed byapplying and baking an electrically conductive paste, a heating elementis used and made adjacent to electrodes 12(A1) and 12(A2).

As shown in FIG. 19, a protection element 160 comprises: an insulatingsubstrate 11; a heating element 161 mounted on a front surface 11 a ofthe insulating substrate 11; electrodes 12(A1) and 12(A2) formed on thefront surface 11 a of the insulating substrate 11 so as to be adjacentto the heating element 161; a heating body extraction electrode 16laminated between the electrodes 12(A1) and 12(A2) on the front surface11 a of the insulating substrate 11 and electrically connected to theheating element 161; and a fusible conductor 13 each end of which isconnected to the corresponding one of electrodes 12(A1) and 12(A2) and acenter portion of which is connected to the heating body extractionelectrode 16. The protection element 160 has the same configuration asthe above-mentioned protection element 80 has, except that, in place ofthe heating body 14, a heating element 161 is connected to the heatingbody extraction electrode 16 laminated on the front surface 11 a of theinsulating substrate 11 and is also connected to a heating elementelectrode 162. The heating element 161 is mounted on a land portion 163formed on the front surface 11 a of the insulating substrate 11.

In the protection element 160, the heating element electrode 162 isconnected to the above-mentioned current control element 27, whereby,when an abnormal voltage is detected in any one of the battery cells 21to 24, the heating element 161 is operated to interrupt acharge-and-discharge path of the battery stack 25.

Also in the protection element 160, the heating element 161 is laminatedon the front surface 11 a of the insulating substrate 11 so as to beadjacent to the electrode 12(A1), whereby the front surface 11 a of theinsulating substrate 11 is made flat, and thus the heating bodyextraction electrode 16 can be formed on the same plane as theelectrodes 12(A1) and 12(A2). Furthermore, in the protection element160, the heating body extraction electrode 16 is made to have the sameheight as the electrodes 12 (A1) and 12 (A2) have, whereby the fusibleconductor 13 can be made flat to be connected thereto. Therefore, in theprotection element 160, fusion characteristics of the fusible conductor13 can be improved.

Furthermore, in the protection element 160, the heating element 161 islaminated so as to be adjacent to the electrodes 12(A1) and 12(A2),whereby a generated heat can be efficiently transferred to the fusibleconductor 13, and thus the fusible conductor 13 can be heated as is thecase where the heating body 14 is superimposed with the heating bodyextraction electrode 16 via the insulating member 15.

Furthermore, in the protection element 160, an electrically conductivepaste to constitute the electrodes 12(A1) and 12(A2) and the heatingbody extraction electrode 16 is applied to the front surface 11 a of theflat insulating substrate 11, whereby the electrodes 12(A1) and 12(A2)and the heating body extraction electrode 16 can be collectively formed,and thus the reduction of labor in a manufacturing process can beachieved. Furthermore, the protection element 160 does not have such aconfiguration that the heating body 14 is formed on the front surface 11a of the insulating substrate 11 so as to be superimposed with theheating body extraction electrode 16, and therefore the protectionelement 160 can be miniaturized by the height reduction in a thicknessdirection of the insulating substrate 11.

Furthermore, in the protection element 160, as the heating element 161,there may be used an element selected from various kinds of elements tobe mounted, and capable of generating a heat having a high temperaturesuitable for fusing of the fusible conductor 13.

MODIFIED EXAMPLE 14

FIG. 20A to FIG. 22B illustrate modified examples wherein theconfiguration of the fusible conductor is modified.

A protection element 170 shown in FIG. 20A and FIG. 20B uses a fusibleconductor 173 having a three-layer structure wherein high melting pointmetal layers 172 as external layers are formed on both surfaces of a lowmelting point metal layer 171 as an internal layer. In the fusibleconductor 173, a linear opening portion 172 a is formed in the highmelting point metal layer 172 constituting an external layer, along alongitudinal direction thereof, and the low melting point metal layer171 is exposed from said opening portion 172 a. In the fusible conductor173, the exposure of the low melting point metal layer 171 from theopening portion 172 a allows a contact area of a molten low meltingpoint metal with the high melting point metal layer 172 to be increased,whereby an erosion action of the high melting point metal layer 172 canbe further promoted, thereby improving fusion characteristics. Theopening portion 172 a in the high melting point metal layer 172 can beformed, for example, in such a manner that plating of a metalconstituting the high melting point metal layer 172 is partially appliedto the low melting point metal layer 171.

The protection element 170 has the same configuration as theabove-mentioned protection element 10 has, except that a fusibleconductor 173 is used in place of the fusible conductor 13. The fusibleconductor 173 is connected to the electrodes 12(A1) and 12(A2) and theheating body extraction electrode 16, each being provided with a Ni/Auplating layer 52, via a low melting point metal 134, such as solder.Furthermore, in the fusible conductor 173, a flux 17 is applied on asurface of the high melting point metal layer 172. The high meltingpoint metal layer 172 may be formed by using the same material as thatused for the above-mentioned high melting point metal layer 13 a,meanwhile the low melting point metal layer 171 may be formed by usingthe same material as that used for the above-mentioned low melting pointmetal layer 13 b.

Furthermore, in the fusible conductor 173, solder may be used as a metalto constitute the low melting point metal layer 171, meanwhile a surfaceof the high melting point metal layer 172 may be coated with Au or afilm containing Au as a main component. Thus, in the fusible conductor173, wettability of the solder constituting the low melting point metallayer 171 can be further improved, whereby the erosion action can bepromoted.

A protection element 180 shown in FIG. 21A and FIG. 21B uses a fusibleconductor 183 having a three-layer structure wherein high melting pointmetal layers 182 as external layers are formed on both surfaces of a lowmelting point metal layer 181 as an internal layer. In the fusibleconductor 183, a circular opening portion 182 a is formed over theentire surface of the high melting point metal layer 182 constituting anexternal layer, and the low melting point metal layer 181 is exposedfrom said opening portion 182 a.

Other configurations of the protection element 180 are the same as thoseof the above-mentioned protection element 170. The opening portion 182 aof the high melting point metal layer 182 can be formed, for example, insuch a manner that plating of a metal constituting the high meltingpoint metal layer 182 is partially applied to the low melting pointmetal layer 181.

In the fusible conductor 183, the exposure of the low melting pointmetal layer 181 from the opening portion 182 a allows a contact area ofa molten low melting point metal with the high melting point metal layer182 to be increased, whereby an erosion action of the high melting pointmetal layer 182 can be further promoted, thereby improving fusioncharacteristics.

Furthermore, in the fusible conductor 183, solder may be used as a metalto constitute the low melting point metal layer 181, meanwhile a surfaceof the high melting point metal layer 182 may be coated with Au or afilm containing Au as a main component. Thus, in the fusible conductor183, wettability of the solder constituting the low melting point metallayer 181 can be further improved, whereby the erosion action can bepromoted.

A protection element 190 shown in FIG. 22A and FIG. 22B uses a fusibleconductor 193 having a three-layer structure wherein high melting pointmetal layers 192 as external layers are formed on both surfaces of a lowmelting point metal layer 191 as an internal layer. In the fusibleconductor 193, a plurality of linear opening portions 192 a eachextending in a width direction is formed in the high melting point metallayer 192 constituting an external layer, so as to line up in alongitudinal direction, and the low melting point metal layer 191 isexposed from said opening portions 192 a.

Other configurations of the protection element 190 are the same as thoseof the above-mentioned protection element 170. The opening portions 192a of the high melting point metal layer 192 can be formed, for example,in such a manner that plating of a metal constituting the high meltingpoint metal layer 192 is partially applied to the low melting pointmetal layer 191.

In the fusible conductor 193, the exposure of the low melting pointmetal layer 191 from the opening portions 192 a allows a contact area ofa molten low melting point metal with the high melting point metal layer192 to be increased, whereby an erosion action of the high melting pointmetal layer can be further promoted, thereby improving fusioncharacteristics.

Furthermore, in the fusible conductor 193, solder may be used as a metalto constitute the low melting point metal layer 191, meanwhile a surfaceof the high melting point metal layer 192 may be coated with Au or afilm containing Au as a main component. Thus, in the fusible conductor193, wettability of the solder constituting the low melting point metallayer 191 can be further improved, whereby the erosion action can bepromoted.

MODIFIED EXAMPLE 15

FIGS. 23A and 23B illustrate another modified example wherein theconfiguration of the fusible conductor is modified.

A protection element 200 shown in FIG. 23A and FIG. 23B uses a fusibleconductor 203 in which a low melting point metal layer 201 is arrangedas an upper layer, meanwhile a high melting point metal layer 202 isformed as a lower layer. The fusible conductor 203 is connected toelectrodes 12(A1) and 12(A2) and a heating body extraction electrode 16,each being provided with a Ni/Au plating layer 52, via a low meltingpoint metal 204, such as solder. Thus, the fusible conductor 203 has athree-layer structure comprising the low melting point metal 204, thehigh melting point metal layer 202, and the low melting point metallayer 201, which are arranged on the electrodes 12(A1) and 12(A2) andthe heating body extraction electrode 16.

In the fusible conductor 203, a flux 17 is applied on a surface of thelow melting point metal layer 201. The protection element 200 has thesame configuration as the above-mentioned protection element 10 has,except that the fusible conductor 203 is used in place of the fusibleconductor 13. The high melting point metal layer 202 may be formed byusing the same material as that used for the above-mentioned highmelting point metal layer 13 a, meanwhile the low melting point metallayer 201 may be formed by using the same material as that used for theabove-mentioned low melting point metal layer 13 b.

In the protection element 200, the fusible conductor 203 has athree-layer structure comprising the low melting point metal 204, thehigh melting point metal layer 202, and the low melting point metallayer 201, which are arranged on the electrodes 12(A1) and 12(A2) andthe heating body extraction electrode 16, and therefore an action oferoding the high melting point metal layer 202 by the molten low meltingpoint metal 204 and the molten low melting point metal layer 201 allowsaggregation of the molten conductor on the electrodes 12 (A1) and 12(A2) and the heating body extraction electrode 16 to be furtherpromoted, thereby improving fusion characteristics.

Furthermore, in the protection element 200, the fusible conductor 203can be formed through a simple process of laminating the high meltingpoint metal layer 202 on a surface of the low melting point metal layer201.

Furthermore, in the fusible conductor 203, solder may be used as a metalto constitute the low melting point metal layer 201, meanwhile a surfaceof the high melting point metal layer 202 may be coated with Au or afilm containing Au as a main component. Thus, in the fusible conductor203, the wettability of the solder constituting the low melting pointmetal layer 201 can be further improved, whereby the erosion action canbe promoted.

MODIFIED EXAMPLE 16

FIGS. 24A and 24B illustrate another modified example wherein theconfiguration of the fusible conductor is modified.

A protection element 210 shown in FIG. 24A and FIG. 24B uses a fusibleconductor 215 having a four-layer structure wherein a first high meltingpoint metal layer 211, a first low melting point metal layer 212, asecond high melting point metal layer 213, and a second low meltingpoint metal layer 214 are laminated in the order from top to bottom. Thefusible conductor 215 is connected to electrodes 12(A1) and 12(A2) and aheating body extraction electrode 16, each being provided with a Ni/Auplating layer 52, via the second low melting point metal layer 214.

In the fusible conductor 215, a flux 17 is applied on a surface of thefirst low melting point metal layer 211. The protection element 210 hasthe same configuration as the above-mentioned protection element 10 has,except that the fusible conductor 215 is used in place of the fusibleconductor 13. The first high melting point metal layer 211 and thesecond high melting point metal layer 213 may be formed by using thesame material as that used for the above-mentioned high melting pointmetal layer 13 a, meanwhile the first low melting point metal layer 212and the second low melting point metal layer 214 may be formed by usingthe same material as that used for the above-mentioned low melting pointmetal layer 13 b.

In the protection element 210, an action of eroding the first and secondhigh melting point metal layers 211 and 213 by the molten first andsecond low melting point metal layers 212 and 214 allows aggregation ofthe molten conductors on the electrodes 12(A1) and 12(A2) and theheating body extraction electrode 16 to be further promoted, therebyimproving fusing characteristics between the electrodes 12(A1) and12(A2) and the heating body extraction electrode 16.

Furthermore, when the second low melting point metal layer 214 is madeto serve as a lowest layer, said second low melting point metal layer214 is made to serve also as an adhesive layer to make a connection tothe electrodes 12 (A1) and 12 (A2) and the heating body extractionelectrode 16. It should be noted that the protection element 210 may usea fusible conductor having a four or more layer structure, the structurebeing such that a high melting point metal layer and a low melting pointmetal layer are alternately laminated.

MODIFIED EXAMPLE 17

FIGS. 25A and 25B illustrate another modified example wherein theconfiguration of the fusible conductor is modified.

A protection element 220 shown in FIG. 25A and FIG. 25B uses a fusibleconductor 222 having a single layer comprising only a high melting pointmetal layer 221. The fusible conductor 222 is connected to electrodes12(A1) and 12(A2) and a heating body extraction electrode 16, each beingprovided with a Ni/Au plating layer 52, via a low melting point metal223 such as solder. Thus, in the fusible conductor 222, there is formeda two-layer structure comprising the low melting point metal 223 and thehigh melting point metal layer 221 which are arranged on the electrodes12 (A1) and 12 (A2) and the heating body extraction electrode 16.

In the fusible conductor 222, a flux 17 is applied on a surface of thehigh melting point metal layer 221. The protection element 220 has thesame configuration as the above-mentioned protection element 10 has,except that the fusible conductor 222 is used in place of the fusibleconductor 13. The high melting point metal layer 221 may be formed byusing the same material as that used for the above-mentioned highmelting point metal layer 13 a, meanwhile the low melting point metal223 may be formed by using the same material as that used for theabove-mentioned low melting point metal layer 13 b.

In the protection element 220, the fusible conductor 222 forms atwo-layer structure comprising the low melting point metal 223 and thehigh melting point metal layer 221 which are arranged on the electrodes12 (A1) and 12 (A2) and the heating body extraction electrode 16, andtherefore an action of eroding the high melting point metal layer 221 bythe molten low melting point metal 223 allows aggregation of the moltenconductor on the electrodes 12 (A1) and 12 (A2) and the heating bodyextraction electrode 16 to be further promoted, thereby improving fusioncharacteristics. Hence, the low melting point metal 223 is preferablyformed so as to be thicker than the high melting point metal layer 221in the fusible conductor 222.

Furthermore, in the protection element 220, the fusible conductor 222has a single layer structure comprising only the high melting pointmetal layer 221, and therefore can be formed through a simple process.

It should be noted that, also in the fusible conductor 222, solder maybe used as a metal to constitute the low melting point metal 223,meanwhile a surface of the high melting point metal layer 221 may becoated with Au or a film containing Au as a main component. Thus, in thefusible conductor 222, wettability of the solder constituting the lowmelting point metal 223 can be further improved, whereby the erosionaction can be promoted.

MODIFIED EXAMPLE 18

FIG. 26 illustrates another modified example wherein a plurality offusible conductors is used.

A protection element 230 shown in FIG. 26 is obtained by upsizing afusible conductor 231 so as to increase the rating of the protectionelement 230 for the use of high currents. Here it should be noted thatupsizing of the fusible conductor 231 causes an increase in the volumeof a molten conductor at the time of melting, whereby there is a riskthat the molten conductor aggregates between each of the electrodes12(A1) and 12(A2) and the heating body extraction electrode 16, andthereby the molten conductor cannot be fused.

Therefore, in the protection element 230, a plurality of divided fusibleconductors is used, and also an insulating layer 232 is formed around afusible conductor connecting portion 16 a arranged on the heating bodyextraction electrode 16. For example, as shown in FIG. 26, in theprotection element 230, a first fusible conductor 231 a and a secondfusible conductor 231 b are provided thereby to improve the rating as awhole. The first fusible conductor 231 a and the second fusibleconductor 231 b each are connected to from the electrode 12 (A1) via theheating body extraction electrode 16 to the electrode 12 (A2) by a lowmelting point metal 233, such as solder. Furthermore, the first fusibleconductor 231 a and the second fusible conductor 231 b are arranged soas to be spaced at a predetermined distance from each other.

The first fusible conductor 231 a and the second fusible conductor 231 beach have a layered structure in which a low melting point metal layerconstituting an internal layer is covered with a high melting pointmetal layer constituting an external layer, and, as shown in FIGS. 22Aand 22B, said conductors each are connected to the electrodes 12(A1) and12(A2) and the heating body extraction electrode 16 via the low meltingpoint metal 233. Alternatively, the first fusible conductor 231 a andthe second fusible conductor 231 b each may have a layered structure inwhich a low melting point metal layer and a high melting point metallayer are laminated, and said conductors each may be connected to theelectrodes 12(A1) and 12(A2) and the heating body extraction electrode16 via the low melting point metal layer constituting a lower layer.Alternatively, the first fusible conductor 231 a and the second fusibleconductor 231 b each may have a single-layer structure comprising only ahigh melting point metal layer, and said conductors each may beconnected to the electrodes 12(A1) and 12(A2) and the heating bodyextraction electrode 16 by the low melting point metal 233.Alternatively, the first fusible conductor 231 a and the second fusibleconductor 231 b each may have a configuration in which an opening isprovided to the high melting point metal layer constituting an externallayer, whereby the low melting point metal layer constituting aninternal layer is exposed outward.

In the protection element 230, an insulating layer 232 is formed in anarea between the first fusible conductor 231 a and the second fusibleconductor 231 b on the heating body extraction electrode 16. Theinsulating layer 232 prevents an increase in the volume of a moltenconductor, the increase having been caused by the union of the moltenfirst fusible conductor 231 a and the molten second fusible conductor231 b, and the insulating layer 232 is formed by using a knowninsulating material by a known method.

A flux (not illustrated) is applied on a surface of the fusibleconductor 231. Furthermore, the protection element 230 has the sameconfiguration as the above-mentioned protection element 10 has, exceptthat a plurality of the fusible conductors 231 is used in place of thefusible conductor 13, and the insulating layer 232 is formed around thefusible conductor connecting portion 16 a arranged on the heating bodyextraction electrode 16. In the fusible conductor 231, the high meltingpoint metal layer may be formed by using the same material as that usedfor the above-mentioned high melting point metal layer 13 a, meanwhilethe low melting point metal layer may be formed by using the samematerial as that used for the above-mentioned low melting point metallayer 13 b.

As shown in FIG. 27, in the protection element 230, also in the casewhere the first fusible conductor 231 a and the second fusible conductor231 b are melted, the insulating layer 232 prevents the moltenconductors from running along the heating body extraction electrode 16and combining each other. Thus, in the protection element 230, even inthe case where the whole volume of the fusible conductor 231 isincreased thereby to improve the rating, there can be prevented asituation in which a molten conductor is drawn close to one side byrunning along the heating body extraction electrode 16, therebyaggregating between each of the electrodes 12(A1) and 12(A2) and theheating body extraction electrode 16 and thus not being able to befused, and as a result, the fusible conductor 231 can be surely fused.

It should be noted that, in the protection element 230, the insulatinglayer 232 may be formed also around the fusible conductor connectingportion on the electrodes 12(A1) and 12(A2). Thus, in the protectionelement 230, there can be prevented a situation in which a moltenconductor is drawn close to one side by running along the electrodes12(A1) and 12(A2), thereby aggregating between each of the electrodes12(A1) and 12(A2) and the heating body extraction electrode 16 and thusnot being able to be fused.

Also, in the case where the fusible conductor 231 has a structure inwhich a low melting point metal layer and a high melting point metallayer are laminated, solder may be used as a metal to constitute a lowmelting point metal, meanwhile a surface of the high melting point metallayer may be coated with Au or a film containing Au as a main component.Thus, in the fusible conductor 231, wettability of the solderconstituting the low melting point metal can be further improved,whereby the erosion action can be promoted.

Furthermore, as shown in FIG. 26, in the protection element 230, aninsulating layer 235 may be formed in a longitudinal direction of theelectrodes 12(A1) and 12(A2). The insulating layer 235 prevents a moltenconductor from crossing over the electrodes 12(A1) and 12(A2) andaggregating in an exterior electrode, and is formed outside a connectingarea of the fusible conductor 231 to the electrodes 12(A1) and 12(A2).As shown in FIG. 27, the insulating layer 235 provided in the protectionelement 230 leads to a molten conductor to aggregate on the electrodes12(A1) and 12(A2), thereby preventing the molten conductor from flowingout to an external electrode.

MODIFIED EXAMPLE 19

FIG. 28 illustrates another modified example wherein a plurality offusible conductors is used.

As is the case with the above-mentioned protection element 230, aprotection element 240 shown in FIG. 28 is obtained by upsizing afusible conductor 241 so as to increase the rating of the protectionelement 240 for the use of high currents.

The protection element 240 has a plurality of divided fusible conductorsand also a narrow portion 242 which is formed around a fusible conductorconnecting portion 16 a arranged on a heating body extraction electrode16, the narrow portion 242 being formed so as to be narrower than saidfusible conductor connecting portion 16 a. For example, as shown in FIG.28, in the protection element 240, a first fusible conductor 241 a and asecond fusible conductor 241 b are formed thereby to improve the ratingas a whole. The first fusible conductor 241 a and the second fusibleconductor 241 b each are connected to from an electrode 12(A1) via theheating body extraction electrode 16 to an electrode 12(A2) by a lowmelting point metal 243, such as solder. Furthermore, the first fusibleconductor 241 a and the second fusible conductor 241 b are arranged soas to be spaced at a predetermined distance from each other.

The first fusible conductor 241 a and the second fusible conductor 241 beach have a layered structure in which a low melting point metal layerconstituting an internal layer is coated with a high melting point metallayer constituting an external layer, and, as shown in FIG. 28, saidconductors each are connected to the electrodes 12(A1) and 12(A2) andthe heating body extraction electrode 16 via the low melting point metal243. Alternatively, the first fusible conductor 241 a and the secondfusible conductor 241 b each may have a layered structure in which a lowmelting point metal layer and a high melting point metal layer arelaminated, and said conductors each may be connected to the electrodes12(A1) and 12(A2) and the heating body extraction electrode 16 via thelow melting point metal layer constituting a lower layer. Alternatively,the first fusible conductor 241 a and the second fusible conductor 241 beach may have a single-layer structure comprising only a high meltingpoint metal layer, and said conductors each may be connected to theelectrodes 12(A1) and 12(A2) and the heating body extraction electrode16 via a low melting point metal. Alternatively, the first fusibleconductor 241 a and the second fusible conductor 241 b each may have aconfiguration in which an opening is provided to a high melting pointmetal layer constituting an external layer, whereby a low melting pointmetal layer constituting an internal layer is exposed outward.

In the protection element 240, the narrow portion 242, which is narrowerthan the fusible conductor connecting portion 16 a, is formed in an areabetween the first fusible conductor 241 a and the second fusibleconductor 241 b arranged on the heating body extraction electrode 16.The narrow portion 242 prevents an increase in the volume of a moltenconductor, the increase in volume being caused by the union of themolten first fusible conductor 241 a and the molten second fusibleconductor 241 b, and said narrow portion 242 is formed by printing apredetermined pattern on the heating body extraction electrode 16 andbaking said heating body extraction electrode. Alternatively, the narrowportion 242 may be formed by providing an insulating layer on theheating body extraction electrode 16.

A flux (not illustrated) is applied on a surface of the fusibleconductor 241. Furthermore, the protection element 240 has the sameconfiguration as the above-mentioned protection element 10 has, exceptthat a plurality of the fusible conductors 241 is used in place of thefusible conductor 13, and the narrow portion 242 is formed around thefusible conductor connecting portion 16 a of the heating body extractionelectrode 16. Furthermore, in the fusible conductor 241, a high meltingpoint metal layer may be formed by using the same material as that usedfor the above-mentioned high melting point metal layer 13 a, meanwhile alow melting point metal layer may be formed by using the same materialas that used for the above-mentioned low melting point metal layer 13 b.

As shown in FIG. 29, in the protection element 240, also in the casewhere the first fusible conductor 241 a and the second fusible conductor241 b are melted, the molten conductors do not flow into the narrowerportion 242 but aggregate in the fusible conductor connecting portion 16a which is wider than the narrower portion 242, whereby the moltenconductors are prevented from running along the heating body extractionelectrode 16 to combine each other. Thus, in the protection element 240,even in the case where the whole volume of the fusible conductor 241 isincreased thereby to improve the rating, there can be prevented asituation in which the molten conductors are drawn close to one side byrunning along the heating body extraction electrode 16, therebyaggregating between each of the electrodes 12(A1) and 12(A2) and theheating body extraction electrode 16 and thus not being able to befused, and as a result, the fusible conductor 241 can be surely fused.

It should be noted that, in the protection element 240, the narrowportion 242 may be formed also around the fusible conductor connectingportion arranged on the electrodes 12(A1) and 12(A2). Thus, in theprotection element 240, there can be prevented a situation in which themolten conductors are drawn close to one side by running along theelectrodes 12(A1) and 12(A2), thereby aggregating between each of theelectrodes 12(A1) and 12(A2) and the heating body extraction electrode16 and thus not being able to be fused.

In the case where the fusible conductor 241 has a structure in which alow melting point metal layer and a high melting point metal layer arelaminated, solder may be used as a metal to constitute a low meltingpoint metal, meanwhile a surface of the high melting point metal layermay be coated with Au or a film containing Au as a main component. Thus,in the fusible conductor 241, wettability of the solder constituting thelow melting point metal can be further improved, whereby the erosionaction can be promoted.

Furthermore, also in the protection element 240, an insulating layer 245may be formed in a longitudinal direction of the electrodes 12(A1) and12(A2), as shown in FIG. 28. The insulating layer 245 prevents themolten conductors from crossing over the electrodes 12(A1) and 12(A2)and aggregating in an exterior electrode, and is formed outside aconnecting area of the fusible conductor 241 to the electrodes 12(A1)and 12(A2). As shown in FIG. 29, the insulating layer 245 provided inthe protection element 240 leads to the molten conductors to aggregateon the electrodes 12(A1) and 12(A2), thereby preventing the moltenconductors from flowing out to an external electrode.

REFERENCE SIGNS LIST

10, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180,190, 200, 210, 220, 230, 240 . . . protection element,

11, 41 . . . insulating substrate,

12(A1), 12(A2), 42 . . . electrode,

13, 91, 121 . . . fusible conductor,

13 a, 43 a, 91 a, 121 a . . . high melting point metal layer,

13 b, 43 b, 91 b, 121 b, 121 c . . . low melting point metal layer,

14, 44 . . . heating body,

15, 45 . . . insulating member,

16 . . . heating body extraction electrode,

17, 47 . . . flux,

18(P1), 18(P2), 48 . . . heating body electrode,

20 . . . battery pack,

20 a . . . positive electrode terminal,

20 b . . . negative electrode terminal,

21 to 24 . . . battery cell,

25 . . . battery stack,

26 . . . detection circuit,

27, 31, 32 . . . current control element,

30 . . . charge-and-discharge control circuit,

33 . . . control unit,

35 . . . charging apparatus,

41 a . . . glass layer,

51 . . . accumulation portion,

52 . . . Ni/Au plating layer,

61 . . . opening,

92 . . . low melting point metal layer,

93 . . . plating layer,

95 . . . electrically conductive paste,

132 . . . cover member

1. (Currently Amendment) A protection element, comprising: an insulatingsubstrate; a heating body laminated on the insulating substrate; aninsulating member laminated on the insulating substrate so as to coverat least the heating body; first and second electrodes laminated on theinsulating substrate having the insulating member laminated thereon; aheating body extraction electrode electrically connected to said heatingbody on a current path between the first and second electrodes; and afusible conductor laminated on the heating body extraction electrodeover a range from the heating body extraction electrode to the first andsecond electrodes, and fusing the current path between the first andsecond electrodes by heating, the fusible conductor having a first partthat is in direct contact with the heating body extraction electrode andis separated from the insulating member by the heating body extractionelectrode, and a second part that is not in contact with the heatingbody extraction electrode and is separated from the insulating member bya gap formed between the fusible conductor and the insulating member,wherein the fusible conductor comprises a layered body including atleast a high melting point metal layer and a low melting point metallayer, and wherein the fusible conductor has a coating structureincluding a low melting point metal layer as an internal layer and ahigh melting point metal layer as an external layer, and wherein the lowmelting point metal layer is melted by a heat generated by the heatingbody, whereby, while eroding the high melting point metal layer, the lowmelting point metal layer is drawn close to a side of the first andsecond electrodes and the heating body extraction electrode, and fused,said first and second electrodes and said heating body extractionelectrode each having high wettability for the low melting point metal.2. The protection element according to claim 1, wherein the low meltingpoint metal layer is made of Pb-free solder, meanwhile the high meltingpoint metal layer is made of Ag or Cu, or a metal containing Ag or Cu asa main component.
 3. The protection element according to claim 1,wherein the fusible conductor is connected by a low melting point metalat positions to be connected to the first and second electrodes and theheating body extraction electrode.
 4. The protection element accordingto claim 1, wherein any one plating treatment selected from Ni/Auplating, Ni/Pd plating, and Ni/Pd/Au plating is performed on surfaces ofthe first and second electrodes and the heating body extractionelectrode.
 5. The protection element according to claim 1, wherein aninsulating member layer is provided between the heating body and theinsulating substrate.
 6. The protection element according to claim 1,wherein the low melting point metal layer has a larger volume than thehigh melting point metal layer has.
 7. The protection element accordingto claim 1, wherein the gap comprises air.